Rope drives, for example of cranes or other hoisting devices such as elevators, in which a rope subject to tensile force is wound up onto a hoisting drum and/or is deflected about rope pulleys tend to twist the rope, in particular when the latter is braided or laid from wires. The twist of the rope in this respect is inter alia created due to the multilayer winding on the hoisting drum and due to torque differences between the different wire layers. Rope pulleys which are not in exact alignment with the longitudinal rope direction can also induce twist. The rope then tends to rotate in itself, i.e. to rotate about its longitudinal axis, which can, on the one hand, result in increased wear at the rope itself, but, on the other hand, can also result in a rotation of the lifting hook with rope pulleys and corresponding safety risks due to increased rope wear; with hoisting devices such as cranes, the problem additionally arises that the lifting hook twists and the rope strands cable and then cross and no longer easily untwist, which does not allow any further operation due to increased wear.
To avoid such rope torsion, it is known to install so-called swivels into the rope drive. Such a swivel as a rule designates a connection of two parts which can be subjected to tension, wherein one part can rotate with respect to the other in the axis of the tensile direction. The two swivel parts are therefore rotatable with respect to one another in the direction of the longitudinal rope axis, in particular about an axis of rotation coaxial to said longitudinal rope axis, for example via a roller bearing connection, wherein a rotatable swivel part is rotationally fixedly connected to the rope, while the other swivel part, which is typically in a fixed position, is rotationally fixedly connected in an articulated manner with respect to a rotation about the longitudinal rope axis, for example to a boom of a crane to which the rope is attached via the named swivel. It has also already been proposed to integrate such a swivel into a rope or to connect two rope pieces to one another by such a swivel, cf. DE 20 2005 009 235 U1, in order to be more flexible with respect to the rope pieces to be untwisted. In the last-named case, there is not swivel part which is attached in a fixed position, but rather each of the swivel parts is rotationally fixedly connected to a rope piece and is itself rotatable in this respect.
Even if such swivels are easy to rotate, for example by the use of roller bearings, i.e. if a compensation rotation can take place between the two swivel parts without any larger resistance, a predefined twist power is sometimes required to introduce a compensation rotation. On the other hand, it sometimes occurs with sheeved rope progressions with large rope lengths such as are customary with tower cranes having trolleys, but also with other cranes, that the twist reduction of the rope cannot be passed on via the corresponding rope pulleys of the sheeving. To be able also to reduce even smaller twists of the rope, it has therefore already been proposed to provide such a swivel with a rotary drive with the aid of which the two swivel parts can be rotated in a forced manner relative to one another, cf. DE 39 37 631 A1. Since the twist of the rope is typically reflected in a rotation of the lifting hook with the pulleys, the crane operator can monitor the angular position of the lifting hook and can actuate the rotary drive of the swivel as soon as he recognizes a rotation of the loose lifting hook with pulley.
The recognition of a skewed angular position of the loose lifting hook is, however, not always very simple. This generally also applies to steel ropes which transmit relatively high torsional forces and if the lifting hook can rotate relatively fast. This applies to a particular degree, however, for high-strength fiber ropes composed of synthetic fibers such as aramid fibers (HMPA), aramid carbon fiber composites, high-modulus polyethylene fibers (HMPE) or poly(p-phenylene-2,6-benzobisoxazole) fibers (PBO). Such fiber ropes have a much smaller rotational stiffness than steel ropes so that rope torsion does not result to the same degree in a rotation of the loose lifting hook with pulleys and is in this respect more difficult to recognize. Like a steel rope, however, such a fiber rope is also rotated in the rope drive, which results in more rope damage such as rope buckling, which in particular forms toward the rope end.
Starting from this, it is the underlying object of the present invention to provide an improved swivel of the named type which avoids disadvantages of the prior art and further develops the latter in an advantageous manner. A smaller twist formation should also in particular be remedied faster and twist at ropes having smaller rotational stiffness should be combated better.
It is therefore proposed no longer only to actuate the rotary drive of the swivel on a rotation of the loose rope pulley in the lifting hook, but rather to detect any rope twist directly at the swivel and to set the rotary drive into operation as soon as twist forces or twist torques from the rope act on the swivel or as soon as these twist forces or twist torques reach a specific level. For this purpose, a sensor unit is provided at the swivel which detects effects of the rope twist on the swivel so that the forced rotation of the swivel parts can be controlled very much more precisely. In accordance with the invention, at least one direction of rotation measurement unit is provided at the swivel for the detection of the direction of twist of the rope with respect to the swivel, wherein the rotary drive can be controlled by a control apparatus in dependence on the determined direction of twist such that the swivel part connected to the rope is rotated in the direction of the detected direction of twist. The rope twist is reduced, and optionally almost completely eliminated by such a subsequent rotation of the rotatable swivel part in accordance with the detected direction of rope twist so that the swivel part follows the rope twist. Even smaller rope rotations can be reduced or also ropes with less rotational stiffness such as fiber ropes can be kept largely free of twist by the twist detection at the swivel itself so that a much higher service life can be achieved due to smaller wear.
In an advantageous further development of the invention, the sensor unit provided at the swivel cannot only comprise a direction of rotation sensor, but also a torque gauge for determining the torque induced by the rope twist at the swivel. Such a quantitative determination of the rope twist or its effects on the swivel by amount allows an even more precise control of the rotary drive than is possible using a twist determination only by sign. The angle of rotation to be carried out by the rotary drive or the speed to be carried out can be adapted by magnitude to the level of the detected twist torque, preferably such that the swivel is immediately further rotated a larger amount when a larger twist or a larger torque is detected, whereas only a smaller rotational movement is carried out when a smaller torque is detected. The dependency between magnitude of the torque and the amount of the angle of rotation is, however, not compulsory and can, if it is provided, be adapted to the respective rope used, for example such that the rotational stiffness of the respective rope used is taken into account. If, for example, a steel rope having a high rotational stiffness is used, a smaller rotational movement of the swivel can also be sufficient with higher torques induced at the swivel to eliminate the rope twist. If, however, a high-strength fiber rope is used which has a relatively low rotational stiffness, a larger rotational movement of the swivel can be initiated—in comparison with the steel rope—with a corresponding torque which is detected at the swivel.
The determination of the direction of rotation and/or of the magnitude of the rope twist can generally take place at different points at the swivel. In accordance with an advantageous embodiment of the invention, the direction of rotation measurement unit and/or the torque gauge can be formed between one of the two swivel parts and the rotary drive to detect a bearing reaction on the rope twist at the rotary drive bearing, in particular a rotation of the rotary drive induced by the rope twist with respect to the named swivel part or the inclination thereto with respect to direction and optionally magnitude. The direction of rotation measurement unit and/or the torque gauge can in particular be associated with a torque support, by means of which a rotation of the rotary drive is intercepted with respect to an abutment contour at the named swivel part. If the swivel is rotationally fixedly mounted, for example to attach a crane hoisting rope to a crane boom, the direction of rotation measurement unit and/or the torque sensor can be provided between a rotary drive housing part and an abutment contour at the fixed-position swivel part.
Alternatively or additionally, the direction of rotation measurement unit and/or the torque gauge can also have a sensor element between a connection piece, which is used to connect the rope at the rotatable swivel part, and the named rotatable swivel part. Further alternatively or additionally, such a sensor element can also be integrated in the drive train of the rotary drive, for example between two transmission elements of an interposed transmission.
If the rotary drive is supported against rotation at a swivel part by means of a torque support in the aforesaid manner, in a further development of the invention, the at least one torque support of the rotary drive—or optionally also a plurality of torque supports—can be associated with at least two abutment contours which are fixedly connected to the swivel part to secure or support the torque support and thus the rotary drive in both, i.e. opposite, possible directions of rotation. In this respect, the two abutment contours can advantageously be arranged relative to the at least one torque support such that the rotary drive has rotary clearance with respect to the swivel part, that is can be rotated a small amount onward with respect to the swivel.
In an advantageous further development of the invention, a sensor element can be associated with each of the abutment parts or with each abutment contour to detect the direction of rotation and/or the torque quantitatively when the torque support contacts a respective abutment part. If the torque support contacts the one abutment part, this signals a first direction of rotation of the rope twist, whereas a contact of the torque support at the other abutment contour indicates the opposite direction of rotation. The contact pressure of the torque support against the abutment contour can in this respect be considered as a measure for the magnitude of the induced torque.
To be able to detect the direction of rotation of the swivel and optionally also its magnitude in the sense of a torque amount in a simple manner between the swivel part and the rotary drive housing, it is advantageous for the rotary drive not to be configured as self-locking or for it to be able to be blocked or at least braked so much by a braking device that the torque induced by the rope twist can be converted into a rotation of the drive housing. A braking device can have a preloaded friction brake, for example in the form of a multi-disk brake, which is vented on the putting into operation of the rotary drive.
If the rotary drive is supported at least within limits with respect to the swivel part in the aforesaid manner, for example by means of a torque support between two abutment parts whose spacing exceeds the thickness of the torque support, in a further development of the invention, a braking apparatus can be provided between the swivel part and the rotatably supported drive housing part for braking the rotation of the drive housing with respect to the swivel part and/or an elastic restoring apparatus can be provided for applying a restoring force which attempts to hold back the drive housing with respect to the swivel part in a starting position which can then, however, be overcome by the rope twist. An unstable, hypersensitive or even uncontrolled rotation to and fro of the rotary drive with respect to the swivel part, in particular with respect stationary swivel part is avoided by such a braking apparatus and/or retention apparatus, which would result in an unwanted signal flicker of the direction of rotation measurement unit and/or of the torque gauge.
The named braking apparatus and/or restoring apparatus can, for example, comprise a spring device which attempts to bring the torque support or another rotationally effective support part of the rotary drive into a predefined position.
The invention will be explained in more detail in the following with respect to a preferred embodiment and to associated drawings.